Hi Merelakiss. Welcome to the forum. This is the biggest nightmare of suspension and alignment technicians. Students were not allowed to do this to their vehicles in our shop mainly because of handling and liability concerns. That aside, the ideal thing to do would be to put the truck back to factory ride height, then see if the problem is still there. I'm betting that is not something very practical to do so lets assume the shaking is related to the modifications for now.
The first thing to look at is whether there is a dropped pitman arm on the steering gearbox. Woops, you should have a rack and pinion steering gear on there, right? What you need to look at is how the front wheels were lowered to raise the truck. The least offensive way to do that is to use "drop spindles". Those are spindles that are normal in every way between where they bolt to the upper and lower ball joints, except the axle is cast lower on the part. That makes the two control arms stay in their original geometry. The only thing that will change is the really drastic angles of the cv joints. Raise the vehicle off the ground and support it by the frame, then feel the half shafts as you rotate the tires by hand. If you feel any binding or clunking, jack it up under the lower control arms and see if that clunking is still there. With that much lift, binding joints would be a real good possibility. You can also remove the half shafts to see if the problem goes away.
If the front end was lifted by simply raising the torsion bars, the steering linkages and lower control arms will no longer be sticking straight out. They will be angled down. That will make the bottoms of the tires walk in and out a lot as you go over bumps and dips in the road. It is possible to realign the truck but the alignment will only be good for a vehicle that is static, (not moving), on a hoist. You WILL have severe tire wear due to the geometry of the suspension regardless of how the alignment is set.
If you have lower control arms that are lowered at the mounting bushings, all bets are off. I don't think you will find those available anymore because of all the problems they caused. If you look from the front, you will notice that the inner tie rod end's ball and socket, (it's actually hidden inside that rubber accordion boot) is very nearly inline with the lower control arm's rubber mounting bushings. That makes the steering linkage follow the same arc as the control arm. Any change to that relationship will cause that tire to turn left or right as the truck goes up and down. That is a very unstable condition and is why they don't modify ride height that way anymore.
Look at the angle of the two drive shafts. Those angles were carefully designed in and what used to be a needed, ... Oh, ... Three degrees of drive shaft angle is now closer to 20 degrees. If the problem goes away when carrying a heavy load, start by checking for a binding u-joint on the rear drive shaft.
These are things related to something binding. If this doesn't help, we can also discuss what might be happening to cause the front tires to shimmy, but I suspect a shimmy would happen at higher speeds too.
Wednesday, October 27th, 2010 AT 11:39 PM